The present invention relates to a method and to a device for repairing a guide blade segment, the guide blade segment preferably being fashioned as a twin guide blade segment in a guide blade composite element that has at least two guide blades that are situated between an inner covering strip and/or an outer covering strip and are connected to one another by these, the guide blades also having a nose segment and a rear edge segment.
The technical area of the present invention relates to the repair of guide blade segments that are used in aircraft jet engines. Here, a turbine is constructed from turbine stages that are situated one after the other in the direction of flow. Each turbine stage is provided with stationary guide blades that can be accommodated between an inner cover strip and an outer cover strip, or at least on one of the cover strips. Depending on the specific embodiment of the turbine, what are known as twin guide blade segments may be used, each having two guide blades situated between a corresponding radial segment of the inner cover strip and/or of the outer cover strip, resulting in a component that can be handled individually. The flow channel is defined by the radial intermediate space between the inner cover strip and the outer cover strip through which the hot exhaust gases from the combustion chamber are conducted.
Due to the high temperatures of the gases that come into contact with the guide blades, the guide blade segments are subject to a high degree of material stress. Besides the thermal and chemical stresses, mechanical stresses may also occur as a result of the penetration of foreign bodies into the jet engine, because such bodies may collide with the guide blades, causing surface damage. In order to withstand the named stresses, the guide blade segments are made for example of highly temperature-resistant cobalt-nickel alloys, and are often provided with a surface coating in order to achieve protection against corrosion as well as mechanical protection. In addition, in order to reduce thermal stress cooling ducts are provided both in the nose segment and also in the rear edge segment of the guide blade, separated from one another by a web in the interior of the guide blade.
Despite these precautionary measures for prolonging the useful life of the guide blade segments, the significant stresses may still cause damage to the guide blades, with the result that, depending on the degree of damage, these blades must be exchanged for new blades or repaired blades. Due to the complex construction of the blades, as well as the very valuable and expensive materials used in their construction, it is often advantageous to replace defective guide blade segments that can no longer be used with repaired guide blade segments, with the aim of replacing the blades not only in the composite element as a twin guide blade segment, but of removing individual guide blades from the guide blade segment and replacing them with new or correspondingly repaired guide blades. In this context, the smallest separable unit is the guide blade as such.
A method for repairing guide blade segments is disclosed in patent specification U.S. Pat. No. 6,785,961 B1. This document discloses a method that is used principally for the repair of guide blade segments. Here, the guide blade segments comprise at least two guide blades situated between an inner cover strip and an outer cover strip, and the method comprises the step of separating the guide blades to obtain a first guide blade that can be repaired and a second guide blade that cannot be repaired, the first guide blade being connected to a newly manufactured guide blade and having the same construction as the second guide blade.
U.S. Pat. No. 3,650,635 discloses a method for repairing guide blades of a gas turbine in which a damaged nose segment is removed from the blade profile part and is replaced with a correspondingly formed replacement part. In this method, the removed segment contains only the nose profile and a part connected thereto of the blade profile main part wall, with the result that it is not ensured that the corresponding replacement part, connected to the fitting and connecting wall surfaces created in this way, will exhibit long-term resistance against all occurrent stresses. Damages in the other parts of the guide blade are thus not repairable, so that replacement of an entire guide blade would be required.
From U.S. Pat. No. 4,305,697, a method is known in which a front edge segment is removed from the blade along a cutting line, the cutting line being situated along a preselected path that undergoes relatively low mechanical stress during operation of the blade and that runs through at least one supporting platform, so that, in addition to the front edge area, a part of at least one supporting platform part is cut away that does not however extend up to the front edge of the platform part. This method also has the problem that only a limited partial area of the overall guide blade can be replaced, this partial area being limited to the front edge surface of the guide blade.
The object of the present invention is therefore to create an improved method and a device for the partial replacement of a plurality of partial areas of a guide blade.